I doubt that those are leaf miners which live inside the leaf between the top and bottom layer, not on the outside. Miners leave the leaves with paler blotches or lines. I'd be inclined to suggest scale or waxy aphids. Can you take a sprig to where you bought your plants? Light horticultural oil will often take care of this type of problem insect, but I don't know if this is the right time of year since sometimes horticultural oil can harm new growth. I don't know if this is the case with boxwood, however.

I have the same problem. I think it is the Boxwood Psyllid (Psylla buxi). Not sure what I am going to do about them. Normally, I ignore them and trim the ends a lot in the spring, but this year I didn't trim as much and they are worse. I read that April and May is when you should use horticultural oil. Or an insecticidal soap that doesn't have pyrethrin in it. I do grow organically. So I am thinking about making up a spray from the kitchen with liquid soap, a few drops of oil and some garlic and see how that works. Otherwise, next year I am going to prune hard and dispose of them.

Well when I googled it said that leaf miners' eggs will hatch about now, which is what the white stuff could be, and that they hover around the plants while they mate and lay new eggs? Which is what my critters are
Doing. And the Tiny orange-red flies seem to fit the description. I'll do some more googling though. I had to fly off to Brazil last night but before I left I sprayed with bio-neem. I hope I didn't hurt anything. :(